1. Field of the Invention
The present invention relates to an optical plane waveguide having a core region with a high refractive index provided in a substrate and guiding signal light.
2. Related Background Art
As an optical element for processing, such as branching, an incident light from an input optical fiber and outputting the same to an output optical fiber, an optical plane waveguide is used. The optical plane waveguide comprises a silica substrate provided with a core region having a high refractive index formed therein, and the core region, for example, has a structure for branching the incident light. A light input/output port of the optical plane waveguide is disposed at an end portion of the silica substrate. That is, light incident on the core region of the optical plane waveguide from the input optical fiber propagates through and is branched in the core region, and further the branched light propagates through the core region thereafter so as to be outputted to the output optical fiber.
Recently, the downsizing and integration of the optical plane waveguide are required. For example, a technique disclosed in the Institute of Electronic Information Communication General Assembly C-3-155 in 1998 is for achieving downsizing and further integration for an optical plane waveguide: by increasing the relative refractive index difference of the core region with respect to the substrate to 0.4%, signal light in the core region can be more strongly confined therein, thereby enabling to lessen a radius of curvature of a bent portion of the core region.